Recently, a high dielectric material such as BST, PZT, PLZT, or the like having a dielectric constant more than ten to hundred times that of a conventional dielectric film has been widely used as a dielectric film of highly integrated circuits.
In the case of forming a capacitor using the high dielectric material mentioned above, new materials such as Pt, Ru, RuO.sub.2, Ir, and IrO.sub.2 having relatively good oxidation resistant characteristics compared with a conventional polysilicon electrode, have been adopted as electrode materials.
Accordingly, the high dielectric materials(i.e.,BST, PZT, PLZT, or the like) and the new electrode materials(i.e., Pt, Ru, RuO.sub.2, Ir, and IrO.sub.2) mentioned above have been used to form a capacitor so as to acquire an available capacitance and a low leakage current. However, in this case, the electrode materials are etched due to a cleaning process performed in subsequent processes of forming a metal contact. Also, metal line materials such as Ti react with the electrode materials and diffuse into the electrode materials, thus transforming an upper surface layer of the electrode.
Therefore, to solve above problems, the adhesion materials such as TiN, TiSiN, polysilicon, or the like are used as an adhesion layer so as to cap the upper electrode, disposing an interlayer insulating film thereon.
FIG. 1 is a cross-sectional view showing a conventional semiconductor device having a high dielectric film.
In FIG. 1, a semiconductor substrate is identified with reference number 10, interlayer insulating films 12, 26, a polysilicon plug 14, adhesion metal layers 16, 24, a lower electrode 18, a dielectric film 20, an upper electrode 22, and a metal line 28.
In accordance with above semiconductor device, the adhesion metal layer 24 caps the upper surface of the upper electrode 22 to prevent the upper electrode 22 from being attacked by the metal line 28. However, the adhesion metal line 24 does not have a good dry etch selectivity with respect to the interlayer insulating film 12, 26, thus resulting in difficulty in forming a metal contact.
In other word, the process for forming the metal contact 28 to the semiconductor substrate 10 and to the upper electrode 22 is performed after the interlayer insulating film 26 is deposited over the capacitor. In case of capping the upper electrode 22 with an adhesion material 24 such as TiN, TiSiN, or the like, disposing the interlayer insulating film 26 thereon, so as to improve adhesion between the upper electrode 22 and the interlayer insulating film 26, as shown in FIG. 1, the adhesion material 24 may be over-etched (reference number 30) due to low dry etch selectivity with respect to an oxide layer used as the interlayer insulating film 26.
When the adhesion material 24 is over etched, the metal line material 28, such as Ti directly contacts to the upper electrode 22 and is diffused into the upper electrode 22 in subsequent process, thus transforming the upper surface layer of the upper electrode 22 and degrading the capacitor characteristics.
To solve the problems mentioned above, a polysilicon layer having a good dry etch selectivity with respect to the oxide layer used as for the interlayer insulating film 12, 26 can be adopted as the adhesion material 24. However, in case of the polysilicon layer, the polysilicon layer is deposited on the upper electrode 22 under the high temperature. As a result, the lower adhesion material 16 beneath the lower electrode 18 is easily oxidized under the high temperature, thus increasing dielectric leakage.
Another method has been proposed to solve the problems. The method employs an additional photolithography process, thus forming a metal contact to the semiconductor substrate and to the upper electrode by a different photolithography process. In other word, the metal contact to the semiconductor substrate and the metal contact to the upper electrode are not formed simultaneously by one photolithography process. As a result in this method, it is an inevitable the problem that the cost increases due to additional photolithography process and the process becomes complicated.